The present invention relates to signal analysis and in certain embodiments to spectral envelope estimation from a series of short-time Fourier transforms.
Many signal processing applications require shifting of signal content in the frequency domain. One example is format modification of a signal to turn a female voice into a male voice or vice versa.
Previous methods of pitch modification, for example, assume that the signal is monophonic, as opposed to polyphonic, and that its pitch has been estimated. This restricts the methods to the narrow subset of potential applications dealing with monophonic, pitch-defined, signals such as voice, monophonic instruments and so on. To process polyphonic signals, it would be useful to obtain a time-varying spectral envelope which highlights multiple pitches and facilitates modification of the multiple pitches.